Independently-controlled double-gate (I-gate) transistors are a relatively recent development in semiconductor processing. They have two gates disposed on opposite sides of a channel, each gate capable of being independently controlled. This provides added transistor flexibility and enables, for example, using a single body to form a dynamic random-access memory (DRAM) cell. Tri-gate transistors are another relatively recent development in semiconductor processing. With tri-gate transistors, the gate forms adjacent three sides of a channel region. Tri-gate transistors, particularly when used with a high-k insulator and metal gate, can substantially improve the speed and performance of integrated circuits.
A number of I-gate structures have been proposed. This and other related technology is described at C. Kuo, IEDM, December 2002, following M. Chan Electron Device Letters, January 1994; C. Kuo, IEDM, December 2002, “A Hypothetical Construction of the Double Gate Floating Body Cell;” T. Ohsawa, et al., IEEE Journal of Solid-State Circuits, Vol. 37, No. 11, November 2002; David M. Fried, et al., “High-Performance P-Type Independent-Gate FinFETs,” IEEE Electron Device Letters. Vol. 25, No. 4, April 2004; and David M. Fried, et al., “Improved Independent Gate N-Type FinFET Fabrication and Characterization,” IEEE Electron Device Letters, Vol. 24, No. 9, September 2003. Tri-gate structures are described at, for instance, publication number U.S. 2004-0036127-A1.